When growth hormone travels from the pituitary gland to the liver it stimulates the production of insulin-like growth factors (IGFs), which are polypeptide protein hormones. Though there are a number of varieties, among the various IGFs, IGF1 is of the most interest to weightlifters due to its capacity to stimulate anabolic, muscle-building effects. It is comprised of 70 different inter-connected amino acids and is produced when growth hormone levels in the bloodstream rise, increasing the production of binding proteins. IGF1 is known to be the mediator of growth hormone anabolic effects. As such, the interconnected relationship between IGF1 and growth hormone is frequently referred to as the Growth Hormone/IGF1 Axis.

The growth of skeletal muscle cells (hypertrophy) is largely regulated by at least three identified processes:

Evidence indicates that IGF1 can positively influence each of these mechanisms. Research has shown that an increase of IGF1 in the bloodstreams spurs growth and regeneration by the body’s cells—particularly among skeletal muscle cells, where it is shown to positively impact muscle strength, size and efficiency. Specifically, it contributes to skeletal muscle growth (hypertrophy) by provoking the synthesis of protein while helping to block muscle atrophy.

Other cells that are positively affected by IGF1 include cartilage, liver, kidney, skin tissue, lung, nerve and bone. IGF1 deficiencies can result in stunted growth as well as a host of other related health problems. There are also indications that because it is capable of activating insulin receptors, IGF1 has the ability to complement and enhance insulin’s effects on muscle development. Because IGF1 levels are so closely tied to growth hormone levels, lower levels of growth hormone in the bloodstream correlate to similar reductions in the production of IGF1. As is the case with growth hormone, IGF1 production peaks during childhood and adolescence and declines as we get older.

We know that the ability of muscle cells to bet bigger and stronger is the result of their unique capacity to continuously adapt to the stress of resistance training with weights. Part of the cells’ capability to accomplish this remarkable feat is attributed to muscle precursor cells that reside in and around skeletal muscle cells. These precursor cells are often referred to as satellite cells. For the most part, satellite cells sit dormant until they are called into duty by hormones such as IGF1.

Once activated by IGF1 the satellite cells divide and their nuclei become genetically similar to those found in skeletal muscle cells. This is a process known as differentiation. Once the satellite cells’ nuclei become similar to those of skeletal muscle cells they become critical to muscle growth and development. This is because skeletal muscle cells must increase their number of nuclei in order to grow larger and repair themselves. The larger the muscle, the more nuclei it requires.

Whenever a muscle grows in response to the stress of resistance training with weights, you will always find a correlating increase in the number of nuclei within the skeletal muscle cells.

But this is not the only way that IGF1 facilitates muscle development, growth and repair. IGF1 also interacts with a number of different stress-activated proteins that assist in the regulation of reactions in the muscle cells that maintenance, repair and growth. When IGF1 binds with these various protein receptors it stimulates a host of biological processes that contribute to and regulate muscle cell growth and development.

There are a number of strategies you can employ to stimulate production of IGF1 in your body. First, because it stimulates a strong hormonal response, resistance training with weights will boost production of IGF1. In particular, it induces its most potent anabolic state in skeletal muscle cells during the intense physical stress generated by heavy weight lifting. This is due in part to the fact that lifting heavy weights stimulates the production of growth hormone, which in turn signals the liver to produce IGF1.

Nutrition also has a very strong effect on the body’s ability to manufacture IGF1. For example, a structured regimen that includes occasional fasting combined with periods of undereating has been shown to have a positive impact on the body’s production of IGF1. Note that carb intake has a significant influence on IGF1 production. Evidence indicates that carb consumption should be minimized to one meal per day or immediately after an exercise session. Overall it is important to maintain sufficient calorie intake and increase consumption of omega-3 fatty acids. Omega 3 not only enhances anabolic actions but it also assists in protecting against insulin resistance.